Vehicle systems may include various vacuum consumption devices that are actuated using vacuum. These may include, for example, a brake booster, a fuel vapor canister etc. Vacuum used by these devices may be provided by a dedicated vacuum pump. In still other embodiments, one or more aspirators (alternatively referred to as ejectors, venturi pumps, jet pumps, and eductors) may be coupled in the engine system that may harness engine air flow and use it to generate vacuum.
Since aspirators are passive devices, they provide low-cost vacuum generation when utilized in engine systems. An amount of vacuum generated at an aspirator can be controlled by controlling the motive air flow rate through the aspirator. While aspirators may generate vacuum at a lower cost and with improved efficiency as compared to electrically-driven or engine-driven vacuum pumps, their use in engine intake systems has traditionally been constrained by both available intake manifold vacuum and maximum throttle bypass flow. Some approaches for addressing this issue involve arranging a valve in series with an aspirator, or incorporating a valve into the structure of an aspirator. Such valves may be referred to as aspirator shut-off valves (ASOVs) or aspirator control valves (ACVs). An opening amount of the valve is regulated to control the motive air flow rate through the aspirator, and thereby control an amount of vacuum generated at the aspirator. By controlling the opening amount of the valve, the amount of air flowing through the aspirator and the suction air flow rate can be varied, thereby adjusting vacuum generation as engine operating conditions such as intake manifold pressure change.
One example approach of controlling an aspirator shut-off valve (ASOV) in an engine is shown by Hirooka in U.S. Pat. No. 8,360,739. The ASOV may be opened or closed based on one or more of a temperature of an engine coolant, intake air temperature, and idle speed. The inventors herein have identified a potential issue with the example approach of Hirooka. For example, engine operating parameters may be altered in response to identification of engine degradation conditions. As such, a controller may operate the engine with adjusted parameters to provide a modified engine operation upon detecting component and/or engine degradation. Herein, regulating the ASOV based on engine coolant temperature, intake air temperature, engine speed, etc. may adversely affect the modified engine operation since motive flow through the aspirator can influence air flow into the engine. To elaborate, ASOV control algorithms that are employed during robust engine operation may not be suitable for modified engine operation after component and/or engine degradation has been determined.
The inventors herein have identified an approach to at least partly address the above issue. Accordingly, an example method for an engine is provided, comprising closing an aspirator control valve (ACV) responsive to diagnosing a first engine degradation condition, and opening the ACV in response to diagnosing a second engine degradation condition, the second engine degradation condition being distinct from the first engine degradation condition. Thus, the ACV may be regulated in a distinct manner based on a type of engine degradation condition.
For example, an engine may include an aspirator for passive vacuum generation. In one example, the engine may be naturally aspirated wherein the aspirator may be coupled in a throttle bypass passage across from an intake throttle in an intake passage. In an alternative embodiment, the engine may be a boosted engine including a compressor wherein the aspirator may be coupled to a compressor bypass passage. Motive flow through the aspirator may be regulated by an aspirator control valve (ACV). A controller may activate the ACV between an open position and a closed position based on engine speed when no degradation of the engine or engine components is detected. When an engine degradation condition is detected, the controller may change engine parameters to provide reliable engine operation in the presence of the engine degradation condition. Further, ACV control may be modified in light of the changed engine operation. As an example, the ACV may be closed (from open) when a first engine degradation condition is detected. Herein, the modified engine operation responsive to the first engine degradation condition may include an increase in intake manifold vacuum levels. An example of the first engine degradation condition is a degraded mass air flow sensor. Alternatively, if a second engine degradation condition is detected, the controller may actuate the ACV to a more open position (from a more closed position). Herein, the modified engine operation responsive to the second engine degradation condition may include a decrease in intake manifold vacuum levels. An example of the second engine degradation condition is the intake throttle stuck in an open position.
In this way, motive flow rate through the aspirator may be regulated based on a type of engine degradation condition. ACV control may not be based on parameters such as engine speed, coolant temperature, emission catalyst temperature, etc. following detection of engine degradation. As such, an ACV control algorithm during modified engine operation following detection of engine degradation may be different from an ACV control algorithm during engine operation without engine degradation conditions. By modifying the position of the ACV based on the type of engine degradation, desired engine operation may be continued without adverse effects from excessive air flow via the aspirator. Overall, a more reliable engine operation may be achieved in the presence of engine degradation conditions.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.